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dm-delay: fix a race between delay_presuspend and delay_bio 

[ Upstream commit 6fc45b6ed921dc00dfb264dc08c7d67ee63d2656 ]

In delay_presuspend, we set the atomic variable may_delay and then stop
the timer and flush pending bios. The intention here is to prevent the
delay target from re-arming the timer again.

However, this test is racy. Suppose that one thread goes to delay_bio,
sees that dc->may_delay is one and proceeds; now, another thread executes
delay_presuspend, it sets dc->may_delay to zero, deletes the timer and
flushes pending bios. Then, the first thread continues and adds the bio to
delayed->list despite the fact that dc->may_delay is false.

Fix this bug by changing may_delay's type from atomic_t to bool and
only access it while holding the delayed_bios_lock mutex. Note that we
don't have to grab the mutex in delay_resume because there are no bios
in flight at this point.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Mikulas Patocka 2023-11-29 13:38:43 -05:00 committed by Greg Kroah-Hartman
parent c4d3957510
commit 4241b51f3e
1 changed files with 12 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
drivers/md/dm-delay.c
View File

@ -30,7 +30,7 @@ struct delay_c {
struct workqueue_struct *kdelayd_wq;
struct work_struct flush_expired_bios;
struct list_head delayed_bios;
atomic_t may_delay;
bool may_delay;
struct delay_class read;
struct delay_class write;
@ -191,7 +191,7 @@ static int delay_ctr(struct dm_target *ti, unsigned int argc, char **argv)
INIT_WORK(&dc->flush_expired_bios, flush_expired_bios);
INIT_LIST_HEAD(&dc->delayed_bios);
mutex_init(&dc->timer_lock);
atomic_set(&dc->may_delay, 1);
dc->may_delay = true;
dc->argc = argc;
ret = delay_class_ctr(ti, &dc->read, argv);
@ -246,7 +246,7 @@ static int delay_bio(struct delay_c *dc, struct delay_class *c, struct bio *bio)
struct dm_delay_info *delayed;
unsigned long expires = 0;
if (!c->delay || !atomic_read(&dc->may_delay))
if (!c->delay)
return DM_MAPIO_REMAPPED;
delayed = dm_per_bio_data(bio, sizeof(struct dm_delay_info));
@ -255,6 +255,10 @@ static int delay_bio(struct delay_c *dc, struct delay_class *c, struct bio *bio)
delayed->expires = expires = jiffies + msecs_to_jiffies(c->delay);
mutex_lock(&delayed_bios_lock);
if (unlikely(!dc->may_delay)) {
mutex_unlock(&delayed_bios_lock);
return DM_MAPIO_REMAPPED;
}
c->ops++;
list_add_tail(&delayed->list, &dc->delayed_bios);
mutex_unlock(&delayed_bios_lock);
@ -268,7 +272,10 @@ static void delay_presuspend(struct dm_target *ti)
{
struct delay_c *dc = ti->private;
atomic_set(&dc->may_delay, 0);
mutex_lock(&delayed_bios_lock);
dc->may_delay = false;
mutex_unlock(&delayed_bios_lock);
del_timer_sync(&dc->delay_timer);
flush_bios(flush_delayed_bios(dc, 1));
}
@ -277,7 +284,7 @@ static void delay_resume(struct dm_target *ti)
{
struct delay_c *dc = ti->private;
atomic_set(&dc->may_delay, 1);
dc->may_delay = true;
}
static int delay_map(struct dm_target *ti, struct bio *bio)